Abstract: Fuyu oil layer and Yangdachengzi oil layer，developed in the third and fourth members of Quantou Formation，are two of the major reservoirs of Songliao Basin.However，their lowporosity and extra lowpermeability restrict the exploration and exploitation of the basin.To study the controls of reservoir physical properties and the causes of low permeability reservoirs of the third and fourth members of Quantou Formation in northern Songliao Basin，the influence factors were studied by using 12 062 data of the measured core porosity and permeability.As the results show，the dominant influence factors on reservoir physical properties are diagenesis，following by sedimentary facies.The fundamental causes of lowpermeability are its low compositional maturity，fine particlesize，mini pore throat，high clay matrix content，and strong diagenesis.Nevertheless，the effects of sedimentary facies and diagenesis on reservoir physical properties vary in different diagenetic stages.Particularly，sedimentary facies is the dominant factor in early diagenesis，while diagenesis is a main factor after subperiod A2 of middle diagenetic stage，these two factors influence weighs the same in subperiod A1 of middle diagenetic stage.The sand bodies which development in different sedimentary facies and different diagenesis stages can form different types of reservoirs.